52-01-07 BELL: Applies to All Model 47D1 Helicopters Having 47-661-030-1 Hub Assembly in the Cooling Fan. Refer to Bell Service Bulletin No. 72.
Compliance required at the next 300-hour overhaul, but not later than March 1, 1952.
To reduce the possibility of throwing blades in flight, rework the existing 47-661-030-1 hub and reassemble the fan using the parts provided in the modification kit. (Note: Do not install old fan blades.) Balance modified fan assembly (assigned P/N 47-661-036-5) in accordance with specified erection and maintenance procedure prior to installation.
(Bell Service Bulletin No. 82 covers this same subject.)